Unlike last year, several iPhone models won't be eligible to download the newest iOS when it makes its debut this fall. This trio of models first released in 2018 won't be coming to the iOS 26 party:

Looking at the home screens, the primary difference you'll find is that in iOS 26 the background of the dock and the search option that sits in between the dock and the home screen icons are more transparent and have a sheen to the edges, whereas in iOS 18, these are slightly darker.